In a wireless communications system, a terminal (User Equipment, UE) needs to establish a connection to a network, and this procedure is referred to as a random access procedure. In a Long Term Evolution (LTE) or Long Term Evolution Advanced (LTE-A) system, the random access procedure is classified into a contention-based random access procedure and a non-contention based random access procedure. Two contention-based random access procedures include four steps shown in FIG. 1, and the non-contention based random access procedure includes only the first two steps. For detailed descriptions about FIG. 1, reference may be made to a preface part of the description of embodiments, which is not described herein.
When the LTE or LTE-A system supports a machine type communication (MTC) service, network coverage of LTE or LTE-A needs to be enhanced, that is, information on an LTE or LTE-A network needs to be sent in an enhanced manner. In the prior art, a method for sending, in an enhanced manner, a random access preamble carried by a physical random access channel (PRACH) is repeatedly sending the random access preamble. For related descriptions, reference may be made to the preface part of the description of embodiments, which is not described herein. It can be learned from analysis that, during scrambling on physical downlink control channels (PDCCH) at different repetition levels, a same random access radio network temporary identifier (RA-RNTI) may be used to calculate scrambling code sequences, where the scrambling on the PDCCHs refers to scrambling cyclic redundancy check (CRC) of downlink control information (DCI) carried by the PDCCHs. In this way, when the UE detects the PDCCHs, if a base station sends, in one subframe, downlink control information (DCI) carried by the PDCCHs at different repetition levels and uses a same RA-RNTI when calculating scrambling code sequences for the PDCCHs at different repetition levels, the UE cannot distinguish the PDCCHs at different repetition levels. When detecting the PDCCHs, the UE may consider a PDCCH at another repetition level as a PDCCH of the UE and successfully detect the PDCCH, and further detect a physical downlink shared channel (PDSCH) that carries a random access response (RAR) and is scheduled by using DCI carried by the PDCCH, which may cause the following problems:
A first problem is RAR missed detection. That is, a PRACH resource set corresponding to the PDCCH at another repetition level does not include a PRACH resource used when the UE sends the random access preamble. Therefore, when detecting the PDSCH scheduled by using the DCI carried by the PDCCH, the UE cannot find a Media Access Control (MAC) subheader including a random access preamble index (RAPID) of the random access preamble sent by the UE, and consequently considers that no RAR is received, which causes RAR missed detection, requires the random access preamble to be sent again, and causes power waste of the UE.
A second problem is an RAR false alarm. If the base station does not send the RAR to the UE, when time division multiplexing/frequency division multiplexing (TDM/FDM) is used for random access preambles at different PRACH repetition levels, because a same code resource may be used for different PRACH repetition levels, and the PDSCH scheduled by using the DCI carried by the PDCCH at the another repetition level may carry the MAC subheader including the PAPID of the random access preamble sent by the UE, the UE mistakenly considers, when detecting the PDSCH scheduled by using the DCI carried by the PDCCH, that the UE has detected the RAR, and executes a subsequent procedure for random access, which also causes power waste of the UE.